In silver complex diffusion transfer processes a light-sensitive silver halide material is image-wise exposed, processed in a developer or activator containing a silver complexing agent, and then contacted with a non-light-sensitive image-receiving layer containing development nuclei (also passed through the processing solution). The image-wise exposed silver halide in the light-sensitive material is developed to silver while the unexposed silver halide portions are transferred by diffusion into the receiving layer whereupon they are converted into silver by the action of the developer on the nuclei. Thus a positive image of the original appears on the receiving layer after separation of the image-receiving material from the light-sensitive silver halide material. This process, having been first described in British Patent No. 614155, is now well known. Certain compounds are now conventionally used in such non-light-sensitive image-receiving layers; for example 2-phenyl-5-mercapto-oxadiazole and 5-methylbenzotriazole. These compounds are utilized to control the density and tone of the positive image.
Other toners, such as those described in British Patents 950668 and 1158479, can either accelerate the production of a positive image as compared to an image-receiving layer having no toner added thereto, or as compared to an image-receiving layer with known development retarding toner, for example 1-phenyl-2-tetrazoline-5-thione.
All these compounds, although efficacious in their way, have drawbacks and accordingly the need exists to improve the performance of non-light-sensitive image-receiving layers and in particular to improve the speed of development which would allow a faster "strip time" and improve resolution and exposure latitude by decreasing sideways diffusion of complexed silver.